now that's clean. >> reporter: detective ron parmertor always knew who killed lisa knoefel. and now he thought he understood why. sabrina had told parmertor lisa was about to crush her dream of remaining part of the knoefel family. >> she hated lisa. >> that feels to me like a motive. >> absolutely. >> i hated lisa. but it was only because she was triggering a lot of past issues. >> reporter: but there was more. there was, said sabrina, someone else. >> it's not all my fault. now i take responsibility because i did what i did. and i know it was wrong. but if it weren't for him it would have never happened. "if it weren't for him." >> reporter: sabrina was referring to her foster father kevin. >> i was doing what kevin told me to do. that's what it comes down to. >> reporter: it was an astonishing accusation. sabrina told parmertor kevin had grown to hate lisa even more than she did. it was a feeling she said kevin shared with her slowly, over several months. >> it started through text -- "man, i wish she had, i wish she was dead." or "i can't stand her. she just needs to go."